Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
• First Hour Test – – – – – Wednesday 16 February Bring two No. 2 pencils An eraser (“Do you feel lucky?”) A photo ID Something to write on • Review Session – Tuesday 15 February – Department of Physics and Astronomy Lobby – 5:00 – 7:00 PM – Drop in IQ • Radio, x-ray and infrared radiation are all examples of: • A. Magic • B. Electromagnetic radiation • C. Atoms and molecules • D. Cartoon characters IQ • That’s right! B. is the correct answer! • Modern astronomical observations from ground and space acquire information from the entire electromagnetic spectrum, from shortwavelength gamma-rays to the longest wavelength radio waves. IQ • A hot, blue star emits more energy at every wavelength than does a cool, red star. • True • False IQ • True. The hotter an object, the bluer it appears. • Blue stars are hotter than red stars and emit more energy at every wavelength. • Cool stars appear red because their peak emission is in the red. IQ • The spectrum of a gas cloud illuminated by nearby hot, blue stars is: • A. An absorption spectrum with many bright lines. • B. A continuous spectrum with bright and dark lines. • C. An emission spectrum with many bright lines. • D. A spectrum analyzer with 3 dB rolloffs at each end. IQ • C. is the correct answer (See C., below). Atoms in the cool gas are excited by the blue light. When they excited atoms decay to a lower energy state, they emit light characteristic of the emitting atom. IQ • The Doppler shift (Doppler Effect) makes rapidly receding objects appear redder. • T • F IQ • T. The wavelength of light emitted from a receding object appears to increase, that is, it appears to be redder. • An approaching object will appear bluer because of the Doppler shift. IQ • The speed of light, usually denoted by ‘c,’ is constant. The value of this constant velocity is very nearly 3 X 105 km/s. This means that the speed of light derived from a galaxy moving away from us at 1000 km/s will be slower by: • A. 0% • B. (103 km/s/ 3 X 105 km/s) * 100 = 3.33% • C. 10% • D. 52.5% IQ • The answer is A! The speed of light is a constant, and it does not depend upon the speed of the source. • The wavelength (or frequency) of light does depend upon the speed of the source. This is the Doppler Effect.